This invention relates to an apparatus and method for the transverse folding of webs such as those made into napkins, hankies, or the like. Representative showings of the prior art can be seen in co-owned U.S. Pat. Nos. 1,566,079, 3,689,061 and 3,870,292.
In the process of producing stacks of transverse folded napkins it is necessary to stop the motion of the napkins in the direction parallel to the plane of the napkins. Stopping this motion causes erratic stacking depending upon the velocity of the napkins. This velocity can limit napkin folder operating speed by causing unacceptable stack quality. Historically, the velocity of motion which had to be removed to create a stack of napkins was the same as the velocity of the web entering the machine.
According to the invention, a pair of vacuum equipped rolls are provided with the second roll in the path of travel of the web segment being rotated at a surface speed slower than the first vacuum equipped roll of the pair. I refer to this invention as "slow speed folding rolls".
The slow-speed folding rolls produce a finished napkin velocity in the direction parallel to the plane of the napkins which is significantly less than the velocity of the web entering the machine. This means that:
1. At a given rate of napkin production, the velocity which must be removed from the napkins when they are stacked is significantly reduced yielding improved stack quality with slow-speed folding rolls. PA1 2. If the machine is run at the maximum acceptable finished napkin velocity which yields acceptable stack quality, it will produce more napkins per minute with slow-speed folding rolls.
In addition, reducing the speed of the folding rolls reduces the radial acceleration forces which act to remove the folded napkins from the folding rolls by overcoming the vacuum system forces which act to hold the folded napkins securely on the folding rolls. The vacuum system forces are limited by natural laws which are unavoidable. The slow-speed folding rolls permit higher napkin production rates than conventional folders by reducing the acceleration forces which the limited vacuum forces must overcome.